Effect of rifampin on the pharmacokinetics and pharmacodynamics of prasugrel in healthy male subjects

OBJECTIVE

Prasugrel is a thienopyridine antiplatelet agent for the prevention of atherothrombotic events in patients with acute coronary syndrome undergoing percutaneous coronary intervention. Since cytochrome P450 enzymes CYP3A4 and CYP2B6 play a major role in prasugrel's active metabolite formation, the effect of potent CYP induction by rifampin on the pharmacokinetics of prasugrel and on the pharmacodynamic response to prasugrel was evaluated in healthy male subjects.

RESEARCH DESIGN AND METHODS

This was an open-label, two-period, fixed-sequence study conducted at a single clinical research center. In the first treatment period, subjects received prasugrel as an oral 60-mg loading dose (LD) on the first day followed by ten oral, 10-mg daily maintenance doses. After a 2-week washout period, subjects received oral rifampin alone (600 mg once daily) for 8 days, followed by coadministration of oral rifampin with prasugrel, given as a 60-mg LD on the first day followed by five daily 10-mg MDs. Blood collection for pharmacokinetic and pharmacodynamic analyses occurred after the LD and fifth MD of prasugrel in both periods. CLINICAL TRIAL SYNOPSIS: clinicalstudyresults.org ID #8976

RESULTS

Rifampin coadministration (600 mg daily) did not affect exposure to prasugrel's active metabolite (R-138727). However, at 2 and 4 h after the prasugrel loading dose (60 mg), rifampicin coadministration was associated with a 6-9 percentage point decrease (p < 0.01) in the magnitude of platelet inhibition; similarly, a 5-17 percentage point decrease (p < 0.05) was observed with rifampin coadministration during the prasugrel maintenance dose (10 mg) period. Post hoc in vitro experiments demonstrated a dose-dependent R-138727-rifampin interaction at the P2Y(12) level unrelated to enzyme induction. A limitation of this study is that while results of the in vitro post hoc study indicate a pharmacodynamic interaction with rifampin, the mechanism underlying this interaction has not been elucidated.

CONCLUSIONS

Dose adjustment should not be necessary when prasugrel is administered with CYP inducers since formation of prasugrel's active metabolite is not affected by potent enzyme induction with rifampin.

Common polymorphisms of CYP2C19 and CYP2C9 affect the pharmacokinetic and pharmacodynamic response to clopidogrel but not prasugrel

BACKGROUND

Thienopyridines are metabolized to active metabolites that irreversibly inhibit the platelet P2Y(12) adenosine diphosphate receptor. The pharmacodynamic response to clopidogrel is more variable than the response to prasugrel, but the reasons for variation in response to clopidogrel are not well characterized.

OBJECTIVE

To determine the relationship between genetic variation in cytochrome P450 (CYP) isoenzymes and the pharmacokinetic/pharmacodynamic response to prasugrel and clopidogrel.

METHODS

Genotyping was performed for CYP1A2, CYP2B6, CYP2C19, CYP2C9, CYP3A4 and CYP3A5 on samples from healthy subjects participating in studies evaluating pharmacokinetic and pharmacodynamic responses to prasugrel (60 mg, n = 71) or clopidogrel (300 mg, n = 74).

RESULTS

In subjects receiving clopidogrel, the presence of the CYP2C19*2 loss of function variant was significantly associated with lower exposure to clopidogrel active metabolite, as measured by the area under the concentration curve (AUC(0-24); P = 0.004) and maximal plasma concentration (C(max); P = 0.020), lower inhibition of platelet aggregation at 4 h (P = 0.003) and poor-responder status (P = 0.030). Similarly, CYP2C9 loss of function variants were significantly associated with lower AUC(0-24) (P = 0.043), lower C(max) (P = 0.006), lower IPA (P = 0.046) and poor-responder status (P = 0.024). For prasugrel, there was no relationship observed between CYP2C19 or CYP2C9 loss of function genotypes and exposure to the active metabolite of prasugrel or pharmacodynamic response.

CONCLUSIONS

The common loss of function polymorphisms of CYP2C19 and CYP2C9 are associated with decreased exposure to the active metabolite of clopidogrel but not prasugrel. Decreased exposure to its active metabolite is associated with a diminished pharmacodynamic response to clopidogrel.

Cytochrome P450 3A inhibition by ketoconazole affects prasugrel and clopidogrel pharmacokinetics and pharmacodynamics differently

Prasugrel and clopidogrel inhibit platelet aggregation through active metabolite formation. Prasugrel's active metabolite (R-138727) is formed primarily by cytochrome P450 (CYP) 3A and CYP2B6, with roles for CYP2C9 and CYP2C19. Clopidogrel's activation involves two sequential steps by CYP3A, CYP1A2, CYP2C9, CYP2C19, and/or CYP2B6. In a randomized crossover study, healthy subjects received a loading dose (LD) of prasugrel (60 mg) or clopidogrel (300 mg), followed by five daily maintenance doses (MDs) (15 and 75 mg, respectively) with or without the potent CYP3A inhibitor ketoconazole (400 mg/day). Subjects had a 2-week washout between periods. Ketoconazole decreased R-138727 and clopidogrel active metabolite Cmax (maximum plasma concentration) 34-61% after prasugrel and clopidogrel dosing. Ketoconazole did not affect R-138727 exposure or prasugrel's inhibition of platelet aggregation (IPA). Ketoconazole decreased clopidogrel's active metabolite AUC0-24 (area under the concentration-time curve to 24 h postdose) 22% (LD) to 29% (MD) and reduced IPA 28% (LD) to 33% (MD). We conclude that CYP3A4 and CYP3A5 inhibition by ketoconazole affects formation of clopidogrel's but not prasugrel's active metabolite. The decreased formation of clopidogrel's active metabolite is associated with reduced IPA.

Structure of a secreted aspartic protease from C. albicans complexed with a potent inhibitor: implications for the design of antifungal agents

The three-dimensional structure of a secreted aspartic protease from Candida albicans complexed with a potent inhibitor reveals variations on the classical aspartic protease theme that dramatically alter the specificity of this class of enzymes. The structure presents: (1) an 8-residue insertion near the first disulfide (Cys 45-Cys 50, pepsin numbering) that results in a broad flap extending toward the active site; (2) a 7-residue deletion replacing helix hN2 (Ser 110-Tyr 114), which enlarges the S3 pocket; (3) a short polar connection between the two rigid body domains that alters their relative orientation and provides certain specificity; and (4) an ordered 11-residue addition at the carboxy terminus. The inhibitor binds in an extended conformation and presents a branched structure at the P3 position. The implications of these findings for the design of potent antifungal agents are discussed.

Cholesterol sulfate protects Candida albicans from inhibition by sphingosine in vitro

Sphingosine is known to have potent biological activity, including pronounced anti-microbial action in vitro against Candida albicans and some bacteria. Several sphingosine bases are present in stratum corneum at concentrations several orders of magnitude above those in other tissues. Sphingosine forms an undissociated salt with organic sulfates, however, so that the free sphingosine in the epidermis may be inactivated by the cholesterol sulfate known to be present. To investigate this hypothesis, C. albicans was grown in cultures with graded concentrations of sphingosine added in ethanol. In 1% ethanol, 0.1-100 microgram/ml sphingosine completely prevented growth of the organism for 12 h. All cultures eventually entered log-phase growth and reached limiting density at a rate inversely proportional to sphingosine concentration. When sphingosine was added, together with an equimolar amount of cholesterol sulfate, there was no delay in the onset of growth of the yeast and the rate of growth and final density were similar to control cultures. These results demonstrate that natural ratios of cholesterol sulfate neutralize the anti-microbial activity of sphingosine in vitro. In the epidermis, endogenous cholesterol sulfate is hydrolyzed by sterol sulfatase at the skin surface, where the released sphingosine may resist microbial colonization of the stratum corneum. This mechanism for liberating anti-microbial sphingosine base only at the skin surface may protect the viable epidermis against known cytotoxic effects of free sphingosine.

Self reported snoring and daytime sleepiness in men aged 35-65 years

BACKGROUND

It has been suggested that snoring alone, without conventional sleep apnoea or hypopnoea, may disrupt sleep and produce substantial daytime hypersomnolence. This study addresses this potential relationship.

METHOD

Eight hundred and fifty men, aged 35-65 years, drawn from one general practice were visited at home and asked a range of questions potentially related to sleepiness, snoring, and sleep apnoea; these included inquiries about alcohol and cigarette consumption, nasal stuffiness, shift work, hypnotic or other drug use, and medical diagnoses. In addition, measurements of height, weight, and overnight arterial oxygen saturation were made. The relation between snoring and sleepiness, with allowance made for potentially confounding variables, including sleep apnoea, was assessed by multiple logistic regression.

RESULTS

Positive answers to all questions about sleepiness were correlated significantly with self reported snoring. After potentially confounding variables and any sleep apnoea had been controlled for, positive answers to four questions about inappropriate drowsiness or sleepiness were independently related to snoring. For example, the odds ratio of admitting to "having almost had two or more car accidents while driving due to sleepiness" was 5.8 (95% confidence intervals: 2.7-12.5) in an "often" snorer.

CONCLUSIONS

Although epidemiological associations such as this do not prove a causal relation, the study suggests that snoring (without classical sleep apnoea) may sometimes reduce sleep quality sufficiently to produce substantial daytime drowsiness.

Comparative production and rapid purification of Candida acid proteinase from protein-supplemented cultures

Six Candida spp. that were previously characterized for cutaneous pathogenicity were assessed for Candida acid proteinase (CAP) production in albumin-supplemented, nitrogen-restricted media. C. albicans CAP production was compared in media supplemented with albumin, casein, collagen, hemoglobin, or keratin and in TC medium 199. C. albicans, C. stellatoidea, and C. tropicalis, which are cutaneous pathogens in murine infections, produced 3.3 to 4.7 times more CAP than did the nonpathogens C. parapsilosis and C. guilliermondii. C. krusei, a nonpathogen, produced negligible amounts of enzyme. C. albicans CAP production was similar in each protein-supplemented medium, and only a single acid proteinase was recovered from each one. Rapid CAP purification from culture supernatants was achieved by hollow fiber and stirred cell ultrafiltration followed by Affi-Gel blue and Sephacryl column chromatographies. The highest yield, purity, and specific activity of CAP were obtained from keratin-supplemented medium supernatants, producing 2.86 mg of purified CAP from a 7-liter culture. CAP was characterized as a 41,500-dalton glycoprotein, with a pI of 4.5; a pH range of 2.5 to 5.5; and broad substrate specificity, including that for keratin, denatured collagen, hemoglobin, casein, and albumin. Isolation of CAP also isolated the keratinolytic proteinase of Candida spp. CAP was inhibited by pepstatin A, but not by EDTA or phenylmethylsulfonyl fluoride. Monospecific antibody to CAP was produced in mice and reacted only to the 41,500-dalton protein, as determined by immunoblot analysis. High CAP production by cutaneous pathogenic Candida spp. supports the fact that CAP is a potential virulence factor that may facilitate Candida colonization and invasion of skin. CAP production from keratin-supplemented medium was superior to that from the other media that were tested and yielded sufficient and suitable enzyme for use in immunoassays of CAP antigen and antibody.

Scanning electron microscopy of epidermal adherence and cavitation in murine candidiasis: a role for Candida acid proteinase

Adherence of blastoconidia to epidermal corneocytes is an early event in Candida colonization and infection of the skin. Pathogenic species adhere more avidly than nonpathogenic species, transform to hyphal growth, and invade the stratum corneum of the skin. Adherence was studied by scanning electron microscopy of experimental murine cutaneous Candida infections, using six species of Candida. Candida albicans and C. stellatoidea blastoconidia, applied to newborn mouse skin, adhered to the stratum corneum in greater numbers than other species tested, acquired fibrils and strands of amorphous mucinlike material ("cohesin") between spores and the corneocyte cell surface, formed cavitations in the corneocyte surface, and invaded the corneocyte envelope by hyphal growth at sites distant to the point of blastoconidia attachment. Other species showed little or no adherence, colonization, or cavitation of the corneocyte surface, except C. tropicalis, which showed intermediate results. Pepstatin, an inhibitor of Candida acid proteinase, did not alter adherence or cohesion formation, but inhibited formation of corneocyte cavitations about adherent blastoconidia, suggesting that this enzyme may facilitate adherence/invasion events on skin. Depletion of surface lipids did not alter the formation of cohesin material or the adherence process. Adherence and invasion of epithelium by pathogenic Candida species include the interaction of blastoconidia with an epithelial surface cohesin material that participates in the adherence process. Candida acid proteinase, a keratinolytic enzyme, may participate in the cavitation process of the corneocyte surface by C. albicans.

Adherence of Candida species to human epidermal corneocytes and buccal mucosal cells: correlation with cutaneous pathogenicity

Adherence of microorganisms to epidermal corneocytes may be a prerequisite for cutaneous colonization and infection. Six species of Candida were assayed in vitro for adherence to human epidermal corneocytes and buccal mucosal cells, and compared to previous studies of pathogenicity in a rodent model of cutaneous candidiasis. C. albicans and C. stellatoidea exhibited marked adherence to both epithelial cell types over time, and were cutaneous pathogens in the rodent model. The remaining species showed little or no adherence, and were nonpathogenic to skin. Adherence to corneocytes was not inhibited by ethylenediamine tetraacetic acid, mannan polysaccharide, or concanavalin A lectin. Fresh human serum, but not heat-inactivated serum, inhibited C. albicans adherence by 50%, and was associated with the deposition of complement components, C3 and factor B on blastospores. Adherence to epithelial corneocytes and mucosal cells is a property of pathogenic species of Candida, and may participate in cutaneous colonization and infection mechanisms. Adherence was time-dependent, and did not require divalent cations. Cell wall mannan may participate in the "adhesin" complex. Mannan activation of serum complement and deposition of C3 and factor B on blastospores may provide a protective action by inhibiting Candida adherence to corneocytes.